1. Field of the Invention
This invention relates to gas turbine combustors and in particular to low emissions Nitric Oxide (NOx) combustors that incorporate multiple fuel nozzles, including a central fuel nozzle located within a premix swirler assembly. This fuel nozzle arrangement is typically found in a dual stagexe2x80x94dual mode combustor used in industrial gas turbines for generating electricity. Due to manufacturing and assembly tolerances with mating components, as well as movement during operation, wearing of the central fuel nozzle and mating swirler has been known to occur. The components are typically constructed of similar materials and will therefore wear at a similar rate. This wear is due to the mating surfaces interacting with each other, which is in turn due to relative mechanical movement of the surfaces and differing thermal expansion of these surfaces. Excessive wear can lead to premature replacement of these components at significant expense to the engine operator. Replacement costs for a new central fuel nozzle and premix swirler assembly can easily exceed $10,000 per combustor. For a typical industrial gas turbine, this wear condition could require early replacement costs of over $100,000 per engine. Utilizing the present invention can extend the life of both the central fuel nozzle and mating premix swirler by reducing the amount of wear, for each component, and directing what wear does occur to a replaceable insert within the premix swirler. Application of this invention will increase the length of time in between combustor overhauls, extend component life, and there by reduce maintenance costs to the engine. Overhaul costs to the operator for applying this invention to the combustor are approximately $1,600 per combustor, or only $16,000 for a typical industrial gas turbine.
2. Description of Related Art
A typical gas turbine may contain multiple combustors each of which contain at least one fuel nozzle for injecting fuel, gaseous or liquid, into the combustor. This fuel then mixes with air and reacts to form a hot gas mixture that drives a turbine. The turbine is mechanically connected to a drive shaft, which is coupled to a generator for generating electricity. Components of a combustor are constructed of high-grade material with high temperature capability to withstand the harsh operating environment. Despite the high quality material selection, there are multiple components of a combustor that interact, and these components, through frictional contact with each other, will degrade during engine operation, eventually requiring replacement.
U.S. Pat. No. 5,749,218, addresses a similar area of concern for engagement of a fuel nozzle to a xe2x80x9cfloatingxe2x80x9d mounting ring of a combustor cap assembly. This mounting ring, composed of a harder material than the fuel nozzle, is allowed to float around the nozzle. Under engine operating conditions the mounting ring vibrates against the fuel nozzle, which is typically made of a softer material, such as stainless steel. This vibration and movement causes excessive wear on the fuel nozzle.
The referenced patent discloses the concept of weld build-up on the fuel nozzle with a material that is sacrificial when it is worn by the corresponding mounting ring. Application of this invention has been known to extend the time between scheduled overhauls by as much as 4,000 operating hours, there by reducing the amount of overhaul operations, and as a result, decreasing the amount of time the engine is offline for repairs. The weld build-up process for this application is advantageous because the fuel nozzle described is relatively small in size, easy to overhaul and repair, and the location of the weld build up is not located close to any critical fuel metering orifices. Misapplication of weld build-up material at such orifices would require excessive rework to the fuel nozzles, and could also reduce performance of the fuel nozzle.
Therefore, although the wear reduction means disclosed in U.S. Pat. No. 5,749,218, is adequate for the embodiment disclosed, it is not advantageous for certain other interfaces, such as a central fuel nozzle that engages a fixed swirler assembly.
What is desired is a wear reduction system that provides the cost benefits of the prior art, but does not have the shortcomings related to weld build-up material in orifices.
It is therefore an object of the present invention to reduce the amount of wear exhibited by a center fuel nozzle in a dual stage-dual mode combustor.
Another object of the invention to direct any wear that does occur to a replaceable insert and reduce the amount of wear exhibited by the fuel nozzle.
Accordingly, the present invention operates in a gas turbine combustor with low nitric oxide emissions, wherein the invention pertains to a means of reducing the amount of wear exhibited between a fuel nozzle and its combustion liner interface. Specifically disclosed is a relationship and structure for directing wear associated with manufacturing and assembly tolerances as well as mechanical interaction to a replaceable insert within in a combustion liner.
In accordance with these and other objects, which will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings.